Refrigeration systems such as heat pump systems used for heating and cooling, air conditioning systems used for cooling air, refrigerators and freezers and the like most in use today operate on the so-called vapor compression principle. In these systems, a refrigerant is compressed by a compressor and then passed to a gas cooler (including condensers) to cool and/or condense the compressed refrigerant while at high pressure. The high pressure refrigerant is then passed to an expansion device such as a capillary or an expansion valve and then to an evaporator at a lower pressure where the refrigerant absorbs the latent heat vaporization of the refrigerant and/or sensible heat.
The refrigerant then exits the evaporator and is returned to the inlet of the compressor at low pressure to be compressed so that the cycle can be repeated continuously.
Most such systems include an accumulator somewhere in the path between the evaporator and the compressor which principally serves to contain excess refrigerant to assure that the system is always charged with sufficient refrigerant to operate. Many such systems, particularly those operating on a transcritical refrigerant such as CO2 also include a so-called suction line heat exchanger. Such suction line heat exchangers (also sometimes referred to as internal heat exchangers) may also be found in very large systems employing more or less conventional refrigerants and in systems of more modest size operating with the refrigerant commonly known as R134a. 
A suction line heat exchanger includes two fluid flow paths in heat transfer relation with one another. One of the flow paths typically interconnects the gas cooler of the system with the evaporator at a location upstream of the expansion device and downstream of the gas cooler. The other flow path is located in the path of refrigerant flow between the evaporator and the inlet of the compressor.
In systems using more or less conventional refrigerants, the presence or absence of a suction line heat exchanger depends upon whether the added efficiency produced by the presence of the suction line heat exchanger is sufficient to offset the cost of the suction line heat exchanger itself and whether the system, when installed in its operating environment, can tolerate the bulk, both in terms of volume and in weight, of an additional heat exchanger. A system typical of the latter situation is one that may be employed in a vehicular application such as an automotive air conditioner.
On the other hand, when operating with transcritical refrigerants such as CO2, suction line heat exchangers are considered almost a virtual necessity in spite of their cost, weight or bulk because of the considerable improvement in efficiency that is obtained with them with such refrigerants.
Given modern day concerns for energy and the cost thereof, it is highly desirable that such a refrigeration system be as efficient as possible so as to minimize the expense of energy. The present invention is directed to improving the efficiency of a vapor compression refrigeration system including a suction line heat exchanger by obtaining even higher levels of efficiency than those obtainable with today's technology.